The present invention relates generally to a damper or elastomeric bearing assembly used to control motion and/or vibration in a mechanical system or the like. More specifically, the present invention relates to a flexbeam damper assembly having a transition shim clamp device. The flexbeam damper assembly of the present invention may be used to control, for example, lead-lag motion and/or vibration in the rotor blades of a rotary-wing aircraft or the like, while allowing flapping and/or pitching motion and/or vibration.
The rotor blades of a rotary-wing aircraft or the like typically include a flexbeam member disposed concentrically within a torque tube, sometimes also referred to as a xe2x80x9cpitch casexe2x80x9d. These flexbeam members and torque tubes may be displaced during operation, especially in relation to one another. Such displacement may include lead-lag motion and/or vibration having an arcuate reciprocating path in the plane of the flexbeam member about a central rotor assembly axis perpendicular to the axis of a given rotor blade, flapping motion and/or vibration in an arcuate reciprocating path about a chordwise axis of the central rotor assembly, linear motion and/or vibration in a linear reciprocating direction toward and away from the central rotor assembly along a radially-extending axis of the rotor blades, and pitching motion and/or vibration about a spanwise or radially-extending axis defined by the flexbeam member and/or a rotor blade. Of these motions and/or vibrations, lead-lag motion and/or vibration must be controlled, while flapping and/or pitching motion and/or vibration must be allowed to maintain safe, efficient, and controlled operation of the rotary-wing aircraft or the like.
The flexbeam member and the torque tube of a given rotor blade are typically coupled together using a flexbeam damper assembly, as will be described in greater detail herein. Such a flexbeam damper assembly may include, for example, both a spherical elastomer bearing member and a flat elastomer bearing member coupled together using a transition shim or the like. Preferably, the flat elastomer bearing member has a relatively high cocking stiffness relative to the spherical elastomer bearing member, causing the flat layer(s) of the flat elastomer bearing member to shear due to lead-lag motion, minimizing the tension and compression forces experienced by the flat layer(s). Such tension and compression forces may lead to fatigue and the eventual failure of the flat elastomer bearing member and/or the spherical elastomer bearing member. The spherical layer(s) of the spherical elastomer bearing member, on the other hand, are intended to be relatively low in cocking stiffness to provide relatively low rotor control forces. Thus, the spherical elastomer bearing member provides relatively low control forces.
The cocking stiffness of the flat elastomer bearing member and, accordingly, that seen by the transition shim due to radial loading may be increased by increasing the planar surface area of the flat layer(s) of the flat elastomer bearing member and/or decreasing the elastomer thickness per flat layer of the flat elastomer bearing member. Advantageously, increasing the cocking stiffness experienced by the transition shim due to radial loading limits a degree of freedom of the overall system and increases elastomer life. The measures described above, however, suffer from several drawbacks. Increasing the cocking stiffness of the flat layer(s) of the flat elastomer bearing member requires the use of very thin flat layers joined together using shims. This results in a flat elastomer bearing member with increased height and weight, and one that is prone to other fatigue-related problems, such as cavitation-type failures. Increasing the planar surface area of the flat layer(s) of the flat elastomer bearing member and/or decreasing the elastomer thickness per flat layer of the flat elastomer bearing member increases the size of the space envelope required. Thus, the measures described above are not practical given some applications.
Thus, what is needed are devices and methods that provide a flexbeam damper assembly having overall increased cocking stiffness due to radial loading, without the need for increasing the cocking stiffness and/or increasing the planar surface area of the flat layer(s) of the flat elastomer bearing member. What is also needed is a flexbeam damper assembly utilizing such devices and methods that is relatively simple and cost-effective to manufacture and maintain.
The present invention provides a transition shim clamp device and associated methods that provide a flexbeam damper assembly having substantial precompression of the spherical layer(s) of the spherical elastomer bearing member and overall increased cocking stiffness due to radial loading, without the need for increasing the cocking stiffness and/or increasing the planar surface area of the flat layer(s) of the flat elastomer bearing member. This provides improved elastomer fatigue life in the layer(s) of both the spherical elastomer bearing member and the flat elastomer bearing member. Advantageously, a flexbeam damper assembly utilizing such a transition shim clamp device and associated methods is relatively simple and cost-effective to manufacture and maintain.
In one embodiment of the present invention, a damper assembly includes a spherical elastomer bearing member, wherein the spherical elastomer bearing member is operable for accommodating relative motion and/or vibration, and a flat elastomer bearing member, wherein the flat elastomer bearing member is operable for accommodating relative motion and/or vibration. The damper assembly also includes a substantially rigid transition shim disposed between the spherical elastomer bearing member and the flat elastomer bearing member, wherein the substantially rigid transition shim is operable for coupling the spherical elastomer bearing member to the flat elastomer bearing member. The damper assembly further includes a tension member attached to the substantially rigid transition shim, wherein the tension member is operable for precompressing the spherical elastomer bearing member and increasing the cocking stiffness of the damper assembly.
In another embodiment of the present invention, a damper assembly includes a spherical elastomer bearing member, wherein the spherical elastomer bearing member is operable for accommodating relative motion and/or vibration between a flexbeam member and a torque tube member of a rotor blade of a rotary-wing aircraft, and a flat elastomer bearing member, wherein the flat elastomer bearing member is operable for accommodating relative motion and/or vibration between a flexbeam member and a torque tube member of a rotor blade of a rotary-wing aircraft. The damper assembly also includes a substantially rigid transition shim disposed between the spherical elastomer bearing member and the flat elastomer bearing member, wherein the substantially rigid transition shim is operable for coupling the spherical elastomer bearing member to the flat elastomer bearing member. The damper assembly further includes a tension member attached to the substantially rigid transition shim, wherein the tension member is operable for precompressing the spherical elastomer bearing member and increasing the cocking stiffness of the damper assembly.
In a further embodiment of the present invention, a rotor blade of a rotary-wing aircraft includes a flexbeam member disposed concentrically within a torque tube member. The rotor blade also includes a spherical elastomer bearing member, wherein the spherical elastomer bearing member is operable for accommodating relative motion and/or vibration between the flexbeam member and the torque tube member, and a flat elastomer bearing member, wherein the flat elastomer bearing member is operable for accommodating relative motion and/or vibration between the flexbeam member and the torque tube member. The rotor blade further includes a substantially rigid transition shim disposed between the spherical elastomer bearing member and the flat elastomer bearing member, wherein the substantially rigid transition shim is operable for coupling the spherical elastomer bearing member to the flat elastomer bearing member. The rotor blade still further includes a tension member attached to the substantially rigid transition shim, wherein the tension member is operable for precompressing the spherical elastomer bearing member.
In a still further embodiment of the present invention, a method for damping relative motion and/or vibration between a flexbeam member and a torque tube member includes the steps of providing a spherical elastomer bearing member, wherein the spherical elastomer bearing member is operable for accommodating relative motion and/or vibration, and providing a flat elastomer bearing member, wherein the flat elastomer bearing member is operable for accommodating relative motion and/or vibration. The method also includes the step of disposing a substantially rigid transition shim between the spherical elastomer bearing member and the flat elastomer bearing member, wherein the substantially rigid transition shim is operable for coupling the spherical elastomer bearing member to the flat elastomer bearing member. The method further includes the step of attaching a tension member to the substantially rigid transition shim, wherein the tension member is operable for precompressing the spherical elastomer bearing member and increasing the cocking stiffness of the damper assembly.